public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}
class Solution {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        List<List<Integer>> ret = new ArrayList<>();
        Arrays.sort(nums);
        for (int i=0;i<nums.length;) {
            for (int j=i+1;j<nums.length;) {
                int left = j+1;
                int right = nums.length-1;
                long aim = (long)target-nums[i]-nums[j];
                while (left<right) {
                    int sum = nums[left]+nums[right];
                    if (sum>aim) right--;
                    else if (sum<aim) left++;
                    else {
                        ret.add(Arrays.asList(nums[i],nums[j],nums[left++],nums[right--]));
                        while (left<right&&nums[left]==nums[left-1]) left++;
                        while (left<right&&nums[right]==nums[right+1]) right--;
                    }
                }
                j++;
                while (j<nums.length&&nums[j]==nums[j-1]) j++;
            }
            i++;
            while (i<nums.length&&nums[i]==nums[i-1]) i++;
        }
        return ret;
    }
}